This invention relates generally to screeds on mobile paving machines, and more particularly to powered devices for altering the crown of material being smoothed by the screed.
In prior art powered crown devices, there is a need to provide a fail safe or automatic shut-off mechanism for a manual hydraulic control valve that is used to control a hydraulically driven, power screw, or turnbuckle style, crowning device for an asphalt screed. If the distance of the movement of the power screw extension is not limited in some way, the danger of turning the screw out of the external body (male portion) exists which would result in the center of the screed falling to the ground.
One attempt to solve this problem involved providing a hole near the end of the screws to accept a roll pin which would extend to the major thread diameter of the screw. The limitation here is that the turnbuckle could now be seized with damage to the external turnbuckle body threads caused by forcing the roll pin into those threads. This solution resulted in damaged parts which would most likely have to be replaced.
Another attempt to solve this problem involved providing stops on the screed frame which would limit the crowning motion. The limitation here is that the screed would have to be beefed up to withstand the maximum thrust of the power screw. This system results in added stresses in the screed frame.
The foregoing illustrates limitations known to exist in present power crown devices. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.